2002 rx300 getting p0300 and p0303 codes when it's cold it stumbles so bad it won't accelerate, You can hear it miss fire badly. almost have to keep foot off acellerator to get it to move. On the highway it will run strong, Sure doesnt sound like coil pacs because it sometimes runs okay

 

Welcome to Club Lexus.

If you are sure it is not the coil pack then what else would be the reason .. spark plug?

Dont diagnose by intuition. There are 5 other cylinders, start swapping the coil pack and the plug.

Salim